1. Field of the Invention
The present invention relates to a machining method in which a required machining is effected on a workpiece by holding the workpiece firmly with the aid of holding means and by putting a working tool in contact with the workpiece thus firmly held. Also, the present invention relates to a machining apparatus using such a machining method.
2. Description of Related Art
In a variety of such machining apparatuses a working or machining liquid is directed to the place at which the working tool is put in contact with the workpiece, thereby cooling the working tool-and-workpiece contacting area to improve the machining precision and the quality of the finished products.
FIG. 14 shows one example of such a machining apparatus. It is a dicing apparatus 50 for dicing semiconductor wafers "W". As seen from FIG. 15, a semiconductor wafer "W" is held in a frame "F" with the aid of holding tape "T", and a plurality of so framed semiconductor wafers are contained in a cassette 71.
Each semiconductor wafer "W" has lateral and longitudinal linear passage "S" forming a lattice pattern to define a plurality of rectangular areas, each having a circuit pattern formed thereon.
The semiconductor wafers "W" are transferred from the cassette 71 to a tentative storage place 73 one after another by transporting means 72. Another transporting means 74 sucks a selected framed semiconductor wafer "W" by applying a negative pressure thereto, and then it turns to bring the framed semiconductor wafer "W" from the tentative storage place 73 to a chuck table 58, putting the framed semiconductor wafer "W" thereon. Then, the framed semiconductor wafer "W" is sucked and held there with a negative pressure applied thereto.
Then, the chuck table 58 is moved in the X-direction to put the framed semiconductor wafer "W" just below an alignment unit 75 for detecting each of the lateral and longitudinal linear passage "S", which are to be cut according to the pattern matching process. The chuck table 58 is moved forward again in the X-direction to a cutting station, in which a cutter unit 77 cuts the semiconductor wafer "W" along each and every linear passage "S" with its cutting blade 76 while being supplied with a cutting liquid as a working liquid. Thus, the semiconductor wafer "W" is diced by cutting the lateral and longitudinal linear passage one by one and separated into a plurality of chips.
Referring to FIG. 16, the cutter unit 77 has its cutting blade 76 covered with a blade cover 78. The cutting blade 76 has agglomeration of abrasive grain on its circumference 79 formed with pulverized diamond et al by electro forming. Also, the cutter unit 77 has a spindle 81 rotatably supported in a spindle housing 80 and a pair of nozzles 82a and 82b to sandwich the cutting blade 76 therebetween, as shown in FIG. 17. The cutting blade 76 is fixed to the end of the spindle 81. The nozzles 82a and 82b direct the working liquid to the opposite sides of the cutting blade 76 at the rate of about two liters per minute for cooling the semiconductor wafer "W".
Even though the whole surface of the semiconductor wafer "W" has been wet with the working liquid, and in spite of the continuous supplying of the working liquid to the blade-and-wafer contacting place the semiconductor wafer "W" cannot be cooled well. As a result it is likely to cause cracks or chippings at the edges of the chips made by dicing, thus deteriorating the quality of the finished chips and lowering the machining precision.
Also disadvantageously, a lot of working liquid must be supplied to wash debris away from the cutting area. Disposal of the so contaminated liquid waste despoils the environment.
Lest an insufficient amount of working liquid should be supplied to the wafer-and-blade contacting place an excessive amount of working liquid, which is much more than needed, is liable to be wasted. With a view to improve the quality of finished chips distilled water is used, and the wasting of such an expensive working liquid is disadvantageous from the point of economical view.
Not only the semiconductor wafer dicing apparatus but also any other machining apparatuses using a working liquid continuously flushing to the workpiece-and-blade contacting place have the above described problems in common. Thus, there has been an increasing demand for saving the working liquid without lowering the machining precision and the quality of finished products.